They had extensive literature on what to do when arrested, before the first protest in NYC. They had already lined up The Lawyers Guild, and every protester has been given their number so they can call for legal assistance if they are arrested.
At GAs eg, before staging protests, the issue of arrests was always raised and those willing to be arrested made themselves known as they were asked to do. There was never any shortage of people willing to do so.
You can eg, see the results of the training they engage in regarding what to do when arrested, in most of the video after the cops show up and begin arresting people. The protesters have been instructed to get the names of those arrested and to ask the cops where they are being taken. The badge numbers of cops are recorded by other protesters. In many of the videos you can see the protesters making use of that training.
In fact there was intense discussion, not about how NOT to get arrested, but about how to act and what to do, once it happened. From the beginning they expected arrests and were very prepared for them. I doubt though, that they expected the brutality that occurred especially in Oakland with the near killing of two Iraq War Veterans or the brutality directed at those who were arrested in the jails or the police vans. Not that it was a surprise, and now of course they do expect it.